I got to disagree here. The reason for the top grip is that it is stronger against people who want a high collar grip. Even in a two vs two gripping situation you will be dominant. On top of that the pull is stronger (at least for me). Furthermore, it is easier to disguise a seoi-nage as a grip break attempt.

It could very well be that this also makes the bow and arrow choke more difficult, but it is not the main reason for doing it. At least it isn’t for me.